In this context, we note Woodward's warning that `“cause” might not turn out to be like “entropy” in the sense that it is a notion that it is usefully applicable to physical situations with a certain structure when analyzed at a certain level of description, and not usefully applicable elsewhere,'[1]}. This suggests a possible objection to the functional programme - one might worry that this `certain structure' which makes causal notions `usefully applicable' is simply causal structure, in which case the functional analysis of causation apparently cannot be given in a non-circular way. But the approach we have taken here suggests a natural answer to this objection: the relevant kind of structure is in fact causal order, since the presence of causal order entails that there is a uniquely correct way to understand the situation in causal terms once we select a direction for the underlying bi-order. Thus the functional analysis can be pursued without risk of circularity if we regard it as an analysis of strong causation and we understand the requisite underlying structure in terms of the independent concept of causal order. And if this is accepted, it seems that we should not expect causal models in the traditional sense to be `usefully applicable' in the description of no-signalling quantum processes, since these phenomena do not have the right kind of structure.
